In general, present existing power supply used in a computer that supports ATX motherboard architecture, and an improvement of the ATX motherboard architecture on power source lies in that a start button of the computer is not connected to the power supply but connected to the motherboard directly, and the motherboard will wake up the power supply in a standby mode, such that the power supply can supply electric power required for the operation of the computer. Further, the ATX motherboard architecture can achieve a remote ON/OFF function. In conformity with the ATX motherboard architecture, the power supply should supply stationary power to the power supply itself and the motherboard in a standby mode before the computer is booted. If the start button or the remote ON/OFF signal triggers the motherboard, the motherboard will trigger the power supply by a PS ON/OFF signal to supply primary output power for driving the operation of all computer equipment. To achieve this function, the power supply supporting the ATX motherboard architecture includes a stationary power system for supplying the stationary power and a primary power system for supplying the primary output power, such that the power supply can output the stationary power after receiving external electric power.
With reference to FIG. 1 for a more specific operation of the power supply, the power supply comprises a filter unit 11, a rectification unit 12, a stationary power system 2, a power factor correction circuit 3, and a primary power system 4, wherein the filter unit 11 is connected to a power source 8 for obtaining an input power, and the stationary power system 2 receives a filtered and rectified input power and converts the input power into a stationary power 91 to be output. On the other hand, the rectification unit 12 has a rear end connected to the power factor correction circuit 3 to receive the filtered and rectified input power, and the power factor correction circuit 3 improves the power factor of the electric power by changing the waveforms of current and voltage, and the electric power output by the power factor correction circuit 3 is defined as a modulated power that can be input to the primary power system 4 directly and converted into a primary output power 93. However, the power factor correction circuit 3 and the primary power system 4 are driven by a control unit 5 (or both power factor correction circuit 3 and primary power system 4 have an independent control unit), and the control unit 5 includes digital components such as a microcontroller chip or a programmable encoder provided for controlling and driving purposes, and the digital components must obtain a bias voltage before operated. Therefore, the ON or OFF state of the control unit 5 depends on whether or not the stationary power 91 is obtained and whether or not a PS ON/OFF signal 92 is triggered and turned on. If the control unit 5 has not been turned on yet, the power factor correction circuit 3 and the primary power system 4 cannot be turned on, and the primary power system 4 will stop its operation, and only the stationary power system 2 will be operated in the standby mode. If a user presses a start button of the computer host, an electric signal will be generated and transmitted to a motherboard installed in the computer host, and the motherboard will generate and transmit a PS ON/OFF signal 92 to the power supply to trigger the control unit 5. At that time, the control unit 5 requires the stationary power 91 for its start to drive the power factor correction circuit 3 and the primary power system 4 to operate.
However, if there is no load in the stationary power system 2 in the standby mode, in the event that the control unit 5 is started, a load is added to the stationary power system 2 instantaneously. Before the output power of the stationary power system 2 is modulated, the voltage obtained by the control unit 5 is too low, and the control unit 5 may not be able to start. To assure normal starts of all digital components that require the stationary power 91 for their operation, the stationary power system 2 has an output end connected to a virtual load 6, and the virtual load 6 normally increases the current of the stationary power system 2, such that the voltage drop caused by the start of the control unit 5 will not affect the start of the control unit 5. The normally connected virtual load 6 will incur normal power losses. Therefore, power supply manufacturers tend to develop energy-saving products and the power supplies require an “80PLUS” certification, which is divided into different ranks such as gold, silver, and bronze. Obviously, it is necessary to overcome the normal power consumption of the virtual load 6 to achieve energy saving purpose.